
main(List<String> args) {
  var person = Person("123", age:30);
  print("${person.age}");
}

class Person{
  final String name;
  final int age;
  // : 后可做 表达式操作
  // Person(this.name, {int age = 0}): this.age = age{

  // }
  // 只能做赋值操作{}
  Person(this.name, {this.age = 10});
  // Person(this.age, this.name);
  // Person(this.name):age = 10{

  // }
}